Emergy and Socio-Ecological Principles in Sustainability Assessment: Methodological Considerations...

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Emergy and Socio-Ecological Principles in Sustainability Assessment: Methodological Considerations from a Wastewater

Treatment Case Study

Erik Grönlund, Anders Klang, and Per-Åke Vikman

ABSTRACT

This paper focuses on the methodological aspects for emergy analysis (EA) and socio-ecological principles (SEP) methods that were previously used for sustainability assessment in a wastewater treatment case study (Grönlund et al. 2004). Grönlund et al. (2004) constructed a model of a microalgae wastewater treatment plant (ALGA), located in Sweden at latitude 60°N, and tested it by comparing it to both a conventional three-step treatment plant and a mechanical and chemical treatment plant complemented with a constructed wetland. Based on a chosen framework (the R framework) defining sustainability and sustainable development and the results from the two assessment methods, the ALGA model was considered to have a better position for sustainable development than the other two. In this paper the performance of the methods are compared, including a discussion on how they relate to the concept of sustainability, which reveals different underlying views on the concept of sustainability and uncertainties in the methodological procedures. The SEP method fits well into the chosen framework of sustainability, while the EA method is more open to other definitions of sustainability. Regardless of some fundamental differences between the methods, the ranking of different options were identical in the case study. This result may appear reassuring, but the methodological discussion clearly suggests that more studies are needed on the operationalization of sustainable development and the related tools for its assessment. INTRODUCTION

Grönlund et al. (2004) made an attempt to assess the sustainability of a microalgal wastewater

treatment model (ALGA) by comparing it to two existing treatment plants, using two different assessment methods - emergy analysis (EA) and a socio-ecological principles method (SEP) – in the context of the framework (from here labelled the R framework) for sustainability assessment developed by Robért (2000) and Robért et al. (2002). This paper compares the two methods and their application to sustainability assessment. Sustainability – The Final Frontier…

Many methods for assessing sustainability relate to the general definition of sustainable

development expressed by the Brundtland Commission (1987) as, “development that meets the needs of the present without compromising the ability of future generations to meet their own needs”. This general definition is often quoted, but also often criticized for being too anthropocentric and vague (Carter 2001). Research to determine how to define the “needs” that must be fulfilled has been carried

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Chapter 26. Emergy and Socio-Ecological Principles...

out and often relates to the work regarding basic human needs by Manfred Max-Neef and Abraham Maslow (Håland 1999, Vikman 2001).

Lately sustainability has become an important factor when discussing wastewater treatment techniques. As in many other fields there is no generally accepted method for assessing sustainability of wastewater treatment; many different approaches have been used by different authors. Sustainability of wastewater treatment has been discussed from a life cycle analysis perspective by Bengtsson et al. (1997), from an exergy perspective by Hellström and Kärrman (1997), from an emergy perspective by Björklund (2000), and Geber and Björklund (2001), and from a system analysis perspective by Chen and Beck (1997) and Hellström et al. (2000). THE CASE STUDY

The following case study is reported in full in Grönlund et al. (2004). This section only

provides the minimum information necessary to follow the discussion in part 3. The Compared Wastewater Treatment Plants

In the case study a microalgae wastewater treatment plant model (ALGA), presented below,

was compared to two existing wastewater treatment plants: the Surahammar treatment plant (WWTP) and the Oxelösund treatment plant (TP+CW). These plants are located at approximately latitude 60°N in the middle of Sweden and serve approximately 10,000 persons. The WWTP is a conventional three-step plant, with mechanical treatment, followed by simultaneous biological active sludge treatment and chemical phosphorous precipitation with iron sulfate. The sludge is treated anaerobically in a digester and the biogas produced is used to produce electricity for the treatment plants internal use. The TP+CW uses mechanical treatment followed by chemical precipitation with aluminum sulfate. The sludge is treated anaerobically in a digester. Due to higher demands on nitrogen reduction, the plant was complemented with a wetland of 22 ha, consisting of two parallel systems of shallow vegetated ponds, intermittently loaded. The WWTP and TP+CW were described and evaluated by Björklund et al. (2001) and Geber and Björklund (2001).

The ALGA model was designed to be comparable to the WWTP and the TP+CW. It was, therefore, designed to serve 10,000 people and to operate under the same climatic conditions as the other plants. The main microalgae treatment step, the high-rate pond (HRP), was assumed to perform from late April to early October, about 5.5 months. Therefore, the first pond in the ALGA model, the facultative pond, was designed to have a storage capacity of 6.5 months. The ALGA model was assumed to produce approximately 1 vertical meter of microalgae biomass sludge in the algae settling pond (ASP) per year, which was dewatered (to minimize the transportation of the sludge to landfill) by freeze-thawing on a gravel bed, as was also done to the primary sludge from the facultative pond. A graphic view of the ALGA model is given in Figure 1. The Sustainability Framework

A framework for sustainability principles and for monitoring of sustainable development was

suggested by Robèrt (2000) and Robèrt et al. (2002) (here labeled the R framework). According to this framework, five hierarchical levels can be identified and should be distinguished when discussing sustainability. The first three R framework levels (RFL) are:

RFL 1. The constitution of the system (e.g. ecological and social principles). RFL 2. A favorable outcome of planning within the system (principles of sustainability). RFL 3. The process to reach the favorable outcome (sustainable development). A plan of action is developed to attain the favorable outcomes.

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The fourth level (RFL 4) is the action level, which includes recycling and switching to renewable energy. The fifth level (RFL 5) is the monitoring and audit level, where, for example, indicators are used to determine if RFL 4 actions are in compliance with principles for the desirable process set up at RFL 3 and to determine the status of the system. The two methods for assessing sustainability used in this case study are both part of RFL 5. The Socio- Ecological Principles (SEP) Method

One of the chosen methods is based on the four socio-ecological principles or systems

conditions (hereafter named SCs) given by Holmberg et al. (1996), which state that: In a sustainable society, nature is not subject to systematically increasing,

SC 1. concentrations of substances extracted from the earth's crust, SC 2. concentrations of substances produced by society, SC 3. degradation by physical means (decreasing biocapacity),

and, in that society: SC 4. human needs are met world-wide.

These SCs are part of level 2 (RFL 2) in the R framework described above, but Azar et al. (1996) have suggested that the SCs can be used as a basis for developing indicators to evaluate and monitor

Figure 1. The ALGA model – graphic view of area relations. Figure from Grönlund et al. (2004).

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sustainability and sustainable development at the 5th level (RFL 5). This is done by assessing to what degree an activity violates each of the four SCs. The activity that least violates the four SCs is considered to be in a better position to initiate or continue a process of sustainable development (RFL 3), leading to sustainability (RFL 2).

The SC 1 implies that rare elements in the ecosphere often cause trouble, even if taken from the lithosphere in only small amounts. It also implies that large amounts from the lithosphere of substances common in the ecosphere also often cause trouble. Azar et al. (1996) suggest the use of lithospheric extraction rates (human extraction per natural weathering and volcanic activity) and accumulated lithospheric extraction (accumulation in the technosphere compared to ecospheric content) as possible indicators to estimate the status of SC 1. For the sustainability analysis in this case, indicators of the former type were used in a quantitative method to assess which of the three suggested treatment systems violates the SC 1 the most (Grönlund et al. 2004).

SC 2 points to substances produced in the technosphere, foreign to nature’s decomposing and recirculation system, and therefore often persistent and accumulative in nutrient chains and loops. SC 2 also refers to substances that exist naturally, but for which the anthropogenic emissions threaten to disturb or disrupt natural cycles. Indicators relating anthropogenic production of these substances to natural production have been suggested as one way of monitoring this aspect of sustainability (Azar et al. 1996). The underlying assumption is that as long as the anthropogenic production is only a fraction of the amount released from natural production, the risk of environmental damage as a result of anthropogenic influence is low. In the case study, violations of SC 2 were addressed with a qualitative approach (Grönlund et al. 2004). Specifically, attention was paid to the use of chemicals in the wastewater treatment.

SC 3 recognizes that it is not enough to protect the ecosphere systems from increasing amounts of disturbing substances; the system’s size must also be maintained, to not “…reduce the physical conditions for the long-term production capacity in the ecosphere or the diversity of the biosphere” (Azar et al. 1996). To assess a system’s performance in accordance with SC 3, the total area of land changed by human structures was used, as suggested by Azar et al. (1996). That is land covered by concrete, asphalt or other biologically non-productive surfaces.

While the first three conditions concentrate on maintaining life supporting ecosphere systems, the 4th condition complements them, with the recognition of the problems associated with a growing global population and uneven distribution of life-supporting wealth. To meet the needs of people living today with a low standard of living and tomorrow’s increased population, our use of resources must be more efficient and more equally distributed both among and within human societies. Violations of SC 4 were evaluated in a semi-quantitative way by comparing the different systems’ use of available free resources as opposed to the use of human made, unevenly distributed resources (Grönlund et al. 2004). The Emergy Analysis (EA) Method

The emergy evaluation method (Odum 1996) was chosen because there were different

contributing factors important to the wastewater treatment systems and this method is able to compare these different types of inputs with emergy as the common unit. There is no generally accepted method to assess sustainability by emergy evaluation. Many authors discuss sustainability using emergy indices (e.g., total resource use, percent indigenous renewable, percent import). Many of these indices were suggested by Brown and Ulgiati (1997) and Ulgiati and Brown (1998), who also introduced an Emergy Sustainability Index (ESI), which is a ratio between wanted yield and environmental load on the system; the ESI “…indicates if a process provides a suitable contribution to the user with a low environmental pressure.” They claimed that an index “…that incorporates these aspects would shed light on sustainability issues and the fit of human economies with that of the biosphere” (Brown and Ulgiati 1999). Odum and Odum (2001) stated that sustainability, normally viewed as seeking a sustainable steady state, should rather be viewed as adapting to the pulsing of resources. Pulsing seems to be a general design principle for systems on all scales – “the pulsing paradigm” (Odum 1994, Odum

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et al. 1995). Sustainability is then focused on finding the right strategy to persist through the four repeating main phases of pulsing: growth, transition climax, descent, and low-energy restoration (Odum and Odum 2001).

Emergy accounting for the case study was performed according to Odum (1996). The total resource use and two indices, percent local renewable and the Emergy Sustainability Index (ESI) (Brown and Ulgiati 1997; Ulgiati and Brown 1998), were used to assess sustainability. The pulsing view on sustainability of Odum and Odum (2001) was not considered. The alternative showing the least resource use, the highest part of renewable resources, and the highest Emergy Sustainability Index (ESI), was considered to be in a better position to initiate or continue a process of sustainable development according to the R framework. The old baseline of Odum (1996) was used.

Results and Conclusions from the Case Study

Using two assessment methods – the socio-ecological principles method and emergy analysis – Grönlund et al. (2004) considered the ALGA model as having a better position for sustainable development according to the R framework, than the two comparison treatment plants. SC 1 was calculated least violated by the ALGA model, since its sum of indicator value was about 8 times lower than the other two alternatives (Table 1). The violation against the SC 2 and SC 3 were considered equal for the three alternatives. For SC 2 this was because the toxic substances in the wastewater were modeled equal for all three alternatives and for SC 3 this was because all three alternatives required slightly less than 1 ha of constructions. SC 4 was found least violated by the ALGA model since it used the least unfairly distributed materials such as oil, iron and copper, and was also the most resource efficient solution except when considering land use. Considering all four SCs the ALGA model was found to be the most favorable system from the SEP perspective. In terms of emergy the ALGA model had about half the resource use of the other two alternatives (Table 2) and used the highest proportion of local free environmental resources. The ALGA model also used the most local free environmental resources, and both it and the Oxelösund mechanical-chemical-wetland treatment plant used much more than the Surahammar conventional three-step treatment plant because of the larger area of the ALGA model and the constructed wetland.

Recirculation of nutrients back to society or production of economically viable products from the treatment by-products would strongly influence the sustainability assessment. The ALGA model has a potential advantage due to interesting biochemical contents in the microalgae biomass, depending on what species will become dominant.

METHODOLOGICAL DISCUSSION

General Aspects on Measuring Sustainability

There is no scientific consensus on how to operationalize sustainability, even though this

concept ranks high on the political agenda of many countries. Grönlund et al. (2004) made choices in two steps. First there was a choice of the sustainability definition. The chosen framework by Robèrt (2000) and Robèrt et al. (2002), in this paper labeled the R framework, has a high level of acceptance, given the wide range of authors experienced in addressing sustainability represented in Robèrt et al. (2002). There are, however, other approaches. The R framework assumes that there is a desirable outcome for sustainability that is possible to define as a goal, at least in some aspects, and that sustainable development is the path leading to this outcome. Another view regards sustainability as impossible to describe in terms of end goals. In this case the focus is on the development part. Sustainable development can then be defined as development that is competitive enough to persist in the system. This persistence has two components: the short term component, and the long term

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Table 1. Substances violating the 1st systems condition (SC1) in the SEP method. Indicator values (dimensionless) from Azar et al. (1996). Table from Grönlund et al. (2004). Substance Raw unit per year Recalculated by indicator values

WWTP i

TP+CW j

ALGA

Unit Indicator

values Ind*

WWTP Ind*

TP+CW Ind*

ALGAElectricity (1/3 of total) a 840 1,320 420 GJ 0.0027 2.3 3.6 1.1Oil b 1,020 47.8 30 GJ 130.3 132,907 6,228 3,909Iron – total 20,900 180 60 kg 1.4 29,260 252 84Machinery c 1,140 40 320 kg 1.4 1,596 56 448Copper 125 12.5 1.25 kg 24 3,000 300 30Chemical precipitation d 320,000 430,000 kg 0.26/0.60 84,592 257,992 Concrete e 108,000 118,000 8,810 kg 0.053 5,776 6,311 471Bricks f 1,670 1,780 kg 0.057 96.1 102.4 Gravel f 61,000 kg 0.057 3,510Asphalt g 34,500 5,800 65,500 kg 0.39 13,393 2,252 25,427Rock wool f 325 71.3 2.8 kg 0.057 18.7 4.1 0.16Plastic h 20 147 430 kg 5.2 103.8 762.8 2,232Polymer h - 2,000 - kg 5.2 10,378 Sum of indicator values*weight

270,000 280,000 36,000

a. b. c. d. e.

f. g. h. i. j.

Recalculated as kilograms of extracted uranium, corresponding to the used electricity Recalculated as kilograms of carbon, using carbon content in heating oil. Calculated as iron. Calculated from content of iron and sulfur (WWTP i), and aluminum and sulfur (TP+CW j). Calculated from a mixture of cement and the chemical composition of medium rock from Swedish lithosphere. Calculated as Swedish medium rock (see above) Calculated to consist of 6% bitumen (oil-based) and 94% Swedish medium rock (above). Calculated as carbon, using medium carbon content of common combustible plastics. Surahammar conventional three step plant. Oxelösund mechanical-chemical-wetland plant.

Table 2. Aggregated emergy flows and emergy indices. Table from Grönlund et al. (2004). Flow or Index Surahammar

conventional three step plant

Oxelösund mechanical-

chemical-wetland plant

ALGA model

R, local renewable 0.5 E+15 sej/yr 12.5 E+15 sej/yr 50.0 E+15 sej/yr N, local non-renewable - 0.1 E+15 sej/yr - F, purchased resources from society 2123 E+15 sej/yr 2411 E+15 sej/yr 928 E+15 sej/yr U = R+N+F, total resource use 2123 E+15 sej/yr 2424 E+15 sej/yr 978 E+15 sej/yr EYR = U/F, Emergy Yield Ratio 1.000 1.005 1.054 ELR = (F+N)/R, Environmental Loading Ratio

4246 193 18.6

ESI = EYR/ELR, sustainability index

0.24 E-3 5.2 E-3 57 E-3

% local renewable = R/U 0.02% 0.5% 5.1%

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component. The short time scale component can be expressed as having to be there tomorrow, to also be able to be there in a 100 years. The long time scale component addresses the means to achieve competitiveness, which must not affect the possibilities of being competitive in the long run. For example, this could be agriculture using cheap phosphate fertilizer with high cadmium content to be competitive in the short run, but making the soil hazardous for food production in the long run.

It is our opinion that the R framework, as presented by Robèrt et al. (2002), is goal oriented, but we also realize that a development oriented method can arguably fit into the R framework if the process management tools are defined as tools leading to sustainability and, therefore, RFL 2 and RFL 3 in the R framework are the same. In other words the process of sustainable development is in itself the favorable outcome. However, this view can turn out as just playing with words, so we stick to the above arguing that the R framework is goal oriented.

The second choice made by Grönlund et al. (2004) was the two methods by which to evaluate sustainability. The socio-ecological principles (SEP) method is a goal oriented method and fits easily into the chosen R framework, since it defines sustainability with the system conditions (SCs) and offers the possibility of ranking alternatives by the degree to which they violate the given SCs. From this ranking it is possible to say which alternative is closer to the chosen sustainability definition. The emergy analysis (EA) method only partially fits into the R framework. Grönlund et al. (2004) adapted the EA method to the SEP method’s SC 4 of efficient resource use and the general suggestion from SC 1 and SC 2 of using the highest possible percent of renewable resources. However, in this goal oriented framework Grönlund et al. (2004) had trouble interpreting the Emergy Sustainability Index (ESI). We believe these troubles were caused by the ESI being a development-oriented measure according to the discussion above, which was not made explicit by Grönlund et al. (2004). An emergy paper more obviously using a development-oriented definition of sustainability is Tilley and Swank (2003), who present a definition of sustainability using the Emergy Investment Ratio (EIR) of a process in the context of the regional EIR. Their argument was that the EIR must closely match the regional EIR, neither too large (overuse) or too small (poor utilization). Though highlighting the short time competition part, it is not obvious how such a measure takes into account the implicit assumption of system stability in the long run, for example, by not increasing concentrations of substances harmful to the system dealt with in SC 1 and SC 2 in the SEP method. The ESI deals with this problem by encouraging a maximized yield per investment (Emergy Yield Ratio, EYR) from the system in the numerator, while encouraging as low an environmental load (ELR) as possible in the denominator.

Details of the SEP and EA Methods

As described above the conditions in the SEP method are conditions of sustainability (RFL

2), and the degree of violation against each condition can be used as a measure of how far an activity is from this aspect of sustainability. However, if there are contradictory answers between the four system conditions, the method does not give any guidance on how to weigh these contradictions. Grönlund et al. (2004) met no such contradictions, but it can be questioned if it is correct to estimate that the violation against the third condition (SC 3) is equal between the three compared treatment alternatives. Is it really appropriate to consider a wetland or the different ALGA ponds equal to the land taken out of production, which was probably an agricultural field or forest? If not, the WWTP would take much less land out of production than the wetland and the ALGA ponds. Another methodological problem is the outcome of the nuclear power calculations, since a life cycle perspective is not applied in this approach. Thereby the mining of uranium ore, the processing of the ore (e.g. sulfuric acid use), and the treatment of the radioactive waste (e.g. the copper used to seal the waste for long time periods) are not included in the assessment, influencing the results concerning SC 1. Furthermore, the discussion of risks around nuclear power seems difficult to include in the SEP method.

As pointed out above the EA method does not easily fit into the R framework. So far sustainability approaches evaluated by EA seem to be of the development oriented type mentioned

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above. However, this is not necessarily the only approach using emergy calculations, since it should also be possible to use them in goal oriented frameworks as done by Grönlund et al. (2004). One important characteristic of EA, not found in the SEP methods or in many other methods, is the evaluation of the non-monetary ecosystem contribution to the wastewater treatment plants. The high importance of the economic inputs compared to the material and emergy flows is a striking result of the EA.

On the other hand there are other aspects addressed by the SEP method that are not included in EA. For example, we conclude that EA does not (yet) handle the SC 2 of foreign substances in the biosphere (although it may address SC 2 indirectly in the Environmental Loading Ratio [ELR]). Furthermore, its ability to consider SC 1 of increasing concentrations in the biosphere of hazardous substances from mining, oil and gas production appears limited. The questions of productivity and regenerating capacity, dealt with in SC 3, are more easily addressed within current EA. SC 4, regarding efficiency, is also dealt with in EA; however, it also includes ecosystem services, which are not commonly included in SC 4. The equity part of SC 4 is explicitly discussed with the EA method, especially in the case of fair trade in international exchange (Odum 1996).

Both SEP and EA have the ability to handle scenario approaches, which can be useful when comparing development options. For example, the energy mix used for calculations in this case study represent old energy technology, but the effect of future technology in the energy mix could be studied in a separate scenario. Scenario techniques could also be a way to include the pulsing approach to sustainability (Odum and Odum 2001). This case study only considers landfill use of the microalgal sludge, but scenarios could also address the question of alternative uses for the microalgal sludge, which seems to be an important potential.

From a communication point of view the SEP method has been proven efficient, mainly by the work of The Natural Step organization, which has successfully popularized the method. The EA method has not yet found such a broad audience. The reason for this is sometimes attributed to the fact that part of the foundation for the emergy concept, the energy hierarchy hypothesis (suggested as a 5th law of thermodynamics [Odum 1996]), and the maximum empower hypothesis (suggested as a 4th law of thermodynamics [Odum 1996], and important for the interpretation of the emergy calculations), are not yet as well known and accepted as the 1st and 2nd laws of thermodynamics, which are important foundations for both methods. Pedagogic efforts have been made and are developing also for EA (e.g. Odum et al. 1998), with icon-based modeling software, like EXTEND, as promising examples (Odum and Odum 2000).

CONCLUSIONS

The comparative use of two methods for sustainability assessment has revealed different underlying views on the concept of sustainability and uncertainties in the methodological procedures. Still, the results of the assessments gave the same ranking order between the studied systems for wastewater treatment. This result may appear reassuring, but the methodological discussion clearly suggests that more studies are needed on the operationalization of sustainable development and the related tools for its assessment. ACKNOWLEDGMENTS The discussion part was greatly improved by the stimulating comments from one anonymous reviewer.

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